1. Field of the Invention
The present invention relates to an etchant, and more particularly, to an etchant for an Ag wire, a method for fabricating an Ag wire using the etchant, and a method for fabricating a thin film transistor (TFT) substrate using the etchant.
2. Description of the Related Art
A liquid crystal display (“LCD”), which is one of the most widely used flat panel displays, includes two panels having a plurality of electrodes and a liquid crystal layer interposed therebetween. The LCD applies voltages to the electrodes to rearrange the liquid crystal molecules, thereby adjusting the transmitted amount of incident light.
An LCD including electrodes on respective panels and thin film transistors (“TFTs”) switching the voltages applied to the electrodes is mostly used among various kinds of LCDs. The TFTs are typically provided on one of the two panels. In the LCD, a plurality of pixel electrodes are arranged in a matrix at one panel and a common electrode covers the entire surface of the other panel. An image is displayed on the LCD by applying individual voltages to the respective pixel electrodes. To apply the individual voltages, a plurality of three-terminal TFTs are connected to the respective pixel electrodes, and a plurality of gate lines transmitting signals for controlling the TFTs and a plurality of data lines transmitting voltages to be applied to the pixel electrodes are provided on the panel.
As the display area of the LCD increases, the gate lines and the data lines connected to the TFTs also grow longer, causing an increase in the resistance of a wire. To solve a signal delay problem resulting from the increase in the resistance, the gate lines and the data lines should be formed of a material having as low a resistivity as possible.
Among materials for a wire, Ag has the lowest resistivity. Ag is known to have a resistivity of about 1.59 μΩcm. Thus, by using gate lines and data lines formed of Ag in a practical process, the signal delay problem can be alleviated.
However, due to the poor adhesion of Ag to a lower substrate such as an insulating substrate formed of glass or a semiconductor substrate formed of intrinsic amorphous silicon or doped amorphous silicon, Ag is not easy to deposit and is likely to bring about lifting or peeling of a wire. Moreover, even when an Ag conductive layer is properly deposited on a substrate, an etchant is used to pattern the Ag conductive layer. When using a conventional etchant for patterning, Ag is over-etched or is not etched uniformly, causing lifting or peeling of a wire and degrading the side profile of the wire.
Consequently, there is a need for an etchant that improves the side profile of the wire while maintaining the adhesion of the Ag conductive layer to the substrate during a process of patterning the Ag conductive layer deposited on the substrate.